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avutil/opt: Don't cast when the result might be misaligned 

A pointer conversion is UB if the resulting pointer is not
correctly aligned for the resultant type, even if no
load/store is ever performed through that pointer (C11 6.3.2.3 (7)).

This may happen in opt_copy_elem(), because the pointers are
converted even when they belong to a type that does not guarantee
sufficient alignment.

Fix this by deferring the cast after having checked the type.
Also make the casts -Wcast-qual safe and avoid an indirection
for src.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2024-03-25 14:54:35 +01:00
parent aa7d6520e6
commit c85477f78d
1 changed files with 15 additions and 14 deletions
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29
libavutil/opt.c
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@ -2028,18 +2028,19 @@ void *av_opt_ptr(const AVClass *class, void *obj, const char *name)
static int opt_copy_elem(void *logctx, enum AVOptionType type,
void *dst, const void *src)
{
uint8_t **dst8 = (uint8_t **)dst;
const uint8_t **src8 = (const uint8_t **)src;
if (type == AV_OPT_TYPE_STRING) {
if (*dst8 != *src8)
av_freep(dst8);
if (*src8) {
*dst8 = av_strdup(*src8);
if (!*dst8)
const char *src_str = *(const char *const *)src;
char **dstp = (char **)dst;
if (*dstp != src_str)
av_freep(dstp);
if (src_str) {
*dstp = av_strdup(src_str);
if (!*dstp)
return AVERROR(ENOMEM);
}
} else if (type == AV_OPT_TYPE_BINARY) {
const uint8_t *const *src8 = (const uint8_t *const *)src;
uint8_t **dst8 = (uint8_t **)dst;
int len = *(const int *)(src8 + 1);
if (*dst8 != *src8)
av_freep(dst8);
@ -2052,12 +2053,12 @@ static int opt_copy_elem(void *logctx, enum AVOptionType type,
} else if (type == AV_OPT_TYPE_CONST) {
// do nothing
} else if (type == AV_OPT_TYPE_DICT) {
AVDictionary **sdict = (AVDictionary **)src;
AVDictionary **ddict = (AVDictionary **)dst;
if (*sdict != *ddict)
av_dict_free(ddict);
*ddict = NULL;
return av_dict_copy(ddict, *sdict, 0);
const AVDictionary *sdict = *(const AVDictionary * const *)src;
AVDictionary **ddictp = (AVDictionary **)dst;
if (sdict != *ddictp)
av_dict_free(ddictp);
*ddictp = NULL;
return av_dict_copy(ddictp, sdict, 0);
} else if (type == AV_OPT_TYPE_CHLAYOUT) {
if (dst != src)
return av_channel_layout_copy(dst, src);